diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java
index 07dba80..274e467 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java
@@ -45,6 +45,8 @@
 import org.onosproject.yangutils.datamodel.YangLeaf;
 import org.onosproject.yangutils.datamodel.YangLeafList;
 import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.YangUnion;
 import org.onosproject.yangutils.parser.Parsable;
 import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
 import org.onosproject.yangutils.parser.exceptions.ParserException;
@@ -101,6 +103,12 @@
                 case LEAF_LIST_DATA:
                     bitsNode.setBitsName(((YangLeafList) tmpData).getName());
                     break;
+                case TYPEDEF_DATA:
+                    bitsNode.setBitsName(((YangTypeDef) tmpData).getName());
+                    break;
+                case UNION_DATA:
+                    bitsNode.setBitsName(((YangUnion) tmpData).getName());
+                    break;
                 // TODO typedef, union, deviate.
                 default:
                     throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
index efec3d1..eec78ba 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
@@ -106,7 +106,16 @@
         if (value.equals(UNBOUNDED_KEYWORD)) {
             maxElementsValue = Integer.MAX_VALUE;
         } else if (value.matches(POSITIVE_INTEGER_PATTERN)) {
-            maxElementsValue = Integer.parseInt(value);
+            try {
+                maxElementsValue = Integer.parseInt(value);
+            } catch (NumberFormatException e) {
+                ParserException parserException = new ParserException("YANG file error : " +
+                        YangConstructType.getYangConstructType(MAX_ELEMENT_DATA) + " value " + value + " is not " +
+                        "valid.");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
         } else {
             ParserException parserException = new ParserException("YANG file error : " +
                     YangConstructType.getYangConstructType(MAX_ELEMENT_DATA) + " value " + value + " is not " +
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
index b0a3b69..fc5dfef 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
@@ -35,6 +35,7 @@
 
 import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
 import static org.onosproject.yangutils.datamodel.utils.YangDataModelFactory.getYangTypeDefNode;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
@@ -117,6 +118,11 @@
         // Validate sub statement cardinality.
         validateSubStatementsCardinality(ctx);
 
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, TYPEDEF_DATA);
+
         /*
          * Create a derived type information, the base type must be set in type
          * listener.
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
index 7f4e86b..a4ff8ae 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
@@ -54,6 +54,7 @@
     private static final String DATE_PATTERN = "[0-9]{4}-([0-9]{2}|[0-9])-([0-9]{2}|[0-9])";
     private static final String NON_NEGATIVE_INTEGER_PATTERN = "[0-9]+";
     private static final Pattern INTEGER_PATTERN = Pattern.compile("[-][0-9]+|[0-9]+");
+    private static final String XML = "xml";
     private static final String ONE = "1";
     private static final int IDENTIFIER_LENGTH = 64;
     private static final String DATE_FORMAT = "yyyy-MM-dd";
@@ -102,6 +103,10 @@
             parserException = new ParserException("YANG file error : " +
                     YangConstructType.getYangConstructType(yangConstruct) + " name " + identifierString + " is not " +
                     "valid.");
+        } else if (identifierString.toLowerCase().startsWith(XML)) {
+            parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(yangConstruct) + " identifier " + identifierString +
+                    " must not start with (('X'|'x') ('M'|'m') ('L'|'l')).");
         } else {
             return identifierString;
         }
@@ -175,7 +180,18 @@
             throw parserException;
         }
 
-        return Integer.parseInt(value);
+        int valueInInteger;
+        try {
+            valueInInteger = Integer.parseInt(value);
+        } catch (NumberFormatException e) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                    "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        return valueInInteger;
     }
 
     /**